Method for igniting and / or maintaining plasma using pulsed high-frequency signals, power generator, and plasma apparatus.

Abstract

A method for igniting and / or maintaining a plasma using a pulsed high-frequency signal includes: a) generating a pulsed high-frequency signal; b) changing the frequency of the high-frequency signal according to a frequency sweep and / or changing the amplitude of the high-frequency signal according to a power sweep during a predetermined first time interval (I) within one pulse (10); and / or c) monitoring at least one process parameter of the plasma process; d) determining the relationship of the process parameter to the performed sweep; and e) detecting whether one or more monitored process parameters associated with one or more sweeps each take a predetermined value or are within a predetermined value range.

Description

Technical Field

[0001] The present invention relates to a method for igniting and / or maintaining a plasma by a pulsed high-frequency signal. Furthermore, the present invention relates to a power generator and a plasma device.

Background Art

[0002] In a plasma process using a pulse source, an impedance trajectory that depends on process parameters is executed during one pulse. The purpose is to reliably ignite the plasma and bring it into a suitable state without the need to readjust the impedance matching network.

[0003] How quickly the plasma is ignited and how stable the plasma process is depend on the shape of the pulsed high-frequency signal. FIG. 1a shows a typical transition of the power of the pulsed high-frequency signal. FIG. 1b shows a typical transition of the frequency of the pulsed high-frequency signal, and FIG. 1c shows a typical transition of the magnitude of the reflectance. In the prior art, multi-stage pulses are often used to ignite and operate the plasma, and an attempt is made to ignite the plasma in the first time interval indicated by I in FIGS. 1a, b, and c. For this purpose, energy is supplied to the plasma chamber between the first time interval I and the second time interval II. The time intervals can also be used to achieve different plasma operating states. In the prior art, the power and frequency of the time intervals are at most optimized manually. During the time intervals I and II, the frequency and amplitude of the high-frequency signal are not changed. The durations of the time intervals I and II are also at most optimized to the extent that is manually optimal.

[0004] During the second time interval II, power can be supplied to the plasma process. The frequency and amplitude of the high-frequency signal are determined such that it can be assumed that the plasma is stable and there is impedance matching during the second time interval II.

[0005] The plasma parameters change during the first time interval I. At the start of the first time interval I, the plasma is not ignited, and therefore the impedance is high. At the end of the first time interval I, the impedance approaches the system impedance after plasma ignition. This can be observed by the decrease in the value of the reflection coefficient, as shown in Figure 1c. The change in plasma impedance leads to the impedance trajectory described above. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] U.S. Patent No. 8884523B2 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The object of the present invention is to provide a method and a power generator that can improve plasma ignition and energy supply. [Means for solving the problem]

[0008] According to the present invention, this problem is solved by a method for igniting and / or maintaining a plasma using a pulsed high-frequency signal, the method comprising the following method steps. a) A step of generating a pulsed high-frequency signal, b) The steps of changing the frequency of a high-frequency signal according to a frequency sweep and / or changing the amplitude of a high-frequency signal according to a power sweep during a predetermined first time interval within a single pulse. c) A step of monitoring at least one process parameter of the plasma process, d) A step to determine the relationship between the process parameters and the sweep that was performed, e) A step of detecting whether one or more monitored process parameters related to one or more sweeps take a predetermined value or are within a predetermined range.

[0009] In the spirit of this invention, a high-frequency signal is a signal with a frequency of 1 MHz or higher. Preferably, the high-frequency signal has a frequency in the range of 10 to 100 MHz.

[0010] In the spirit of this invention, a pulsed high-frequency signal is a high-frequency signal whose pulse shape has been modulated. A possible method for generating such a pulsed high-frequency signal is described, for example, in Patent Document 1. The pulsed high-frequency signal can be pulsed at a maximum frequency of 500 kHz. The pulsed high-frequency signal can be pulsed at multiple power levels.

[0011] In the first time interval, the frequency can vary by ±30%, particularly ±20%, preferably ±10%. The amplitude of the high-frequency signal can also vary by ±30%, particularly ±20%, preferably ±10% in the first time interval.

[0012] In the spirit of this invention, sweep is understood as a predetermined change in one quantity over a predetermined period, or a temporal change in one quantity that matches the measured value. "Temporal change" is understood as a change in that quantity over time. Therefore, frequency sweep is a predetermined change in frequency over a predetermined period, for example, a first and / or second time interval, or a change in frequency that matches the measured value. Power sweep is a predetermined change in the amplitude of a high-frequency signal over a predetermined period, for example, a first and / or second time interval, or a change in the amplitude of a high-frequency signal that matches the measured value.

[0013] Determining the relationship between process parameters and the performed sweep may involve the detection of plasma parameters and the execution of the sweep occurring in a temporal relationship, for example, simultaneously or in a temporally overlapping manner. The relationship between process parameters and sweep may involve the process parameters changing depending on the temporal changes in the frequency or amplitude of the high-frequency signal during the sweep. For example, process parameters may change during plasma ignition, where a given frequency and / or amplitude value of the high-frequency signal can be associated with plasma ignition. The relationship between process parameters and sweep can also be determined by a correlation algorithm determining such a relationship.

[0014] Detecting whether each monitored process parameter is at a predetermined value or within a predetermined range can provide an indication of whether the sweep needs to be modified for process improvement, for example, for plasma ignition.

[0015] An evaluation of one or more sweeps can be performed based on their detection, particularly based on the detection in step e). In particular, it is possible to evaluate whether a particular sweep leads to better or worse process behavior compared to a previous sweep. Furthermore, it is also possible to examine at what point during the sweep ignition occurred. The effect of the sweep on one or more process parameters can be determined. These effects may only occur after a certain amount of time, for example, only after the sweep has finished. The relationship between process parameters and sweeps may also be such that the sweep has no effect on the process parameters.

[0016] A sweep can be selected for subsequent pulses and / or for pulses, particularly for a second time interval of the first pulse or further pulses, based on an evaluation of one or more preceding sweeps. Therefore, a modified sweep can be set for subsequent pulses and / or time intervals based on an analysis of previous sweeps. The second time interval may be suitable for the normal operation of the plasma, i.e., plasma maintenance. For this purpose, impedance matching may be present.

[0017] The evaluation may include an inspection of the sweep based on detection, particularly by step e). In particular, this can determine at what point in the sweep the process parameters exhibit a predetermined behavior.

[0018] The duration of the time interval can be adapted based on an evaluation of the subsequent pulse. For example, if plasma ignition is recognized as occurring very early during the frequency sweep or power sweep of the pulse, the first time interval can be shortened for the subsequent pulse. This allows the second time interval, for example, to be extended accordingly, thereby supplying more energy to the plasma.

[0019] During a predetermined second time interval within a pulse, the frequency of the high-frequency signal can be varied according to a frequency sweep, and / or the amplitude of the high-frequency signal can be varied according to a power sweep. This makes it possible to achieve optimal energy supply to the plasma. Preferably, two different sweeps can be performed alternately.

[0020] Steps c) to e) can also be performed in a second time interval. This makes more analytical data available, and allows setting a second time interval for subsequent pulses, or frequency sweep and / or power sweep for the second time interval for subsequent pulses, in order to achieve a predetermined target process parameter value.

[0021] For at least one additional pulse, a different frequency sweep and / or a different power sweep can be used compared to the previous pulse, especially the first pulse. By comparing the situation with the previous pulse, it is possible to determine whether the plasma process has changed, especially whether it has improved or deteriorated. Depending on the result of this analysis, the frequency sweep and / or the power sweep can be adapted for subsequent pulses.

[0022] Different frequency sweeps and / or power sweeps can be set until one or more monitored process parameters reach a predetermined value or a predetermined value range. This can be done until the optimal process parameters are reached. It is also conceivable to change the target value of the process parameter. Thereby, optimization can be performed during the plasma process.

[0023] In a calibration process, a frequency sweep and / or a power sweep suitable for igniting the plasma can be determined. Thereby, appropriate frequency sweeps and / or power sweeps can also be determined outside the plasma process.

[0024] In particular, one or more of the following process parameters can be monitored. The ignition behavior of the plasma, the power loss of the generator that generates the pulsed high-frequency signal, the reflection coefficient, the amplitude of the high-frequency signal, the relative phase between the traveling wave and the backward wave of the pulsed high-frequency signal.

[0025] The analysis is facilitated when the frequency and / or the amplitude are continuously changed during the frequency sweep and / or the power sweep.

[0026] Frequency sweeps and / or power sweeps can have multiple intervals, in which the frequency and / or amplitude are constant. A single interval can contain multiple periods of a high-frequency signal. Essentially, it is possible to observe the high-frequency signal period by period. However, when the signal is generated and measured / detected interval by interval, the detection and control of process parameters are greatly simplified. In this case, the interval consists of multiple periods of the high-frequency signal, and these multiple periods are not distinguished within the interval in terms of the set power and / or frequency.

[0027] At least some of the intervals can be of different lengths, particularly increasing in length as the pulse progresses. For example, the initial interval of the first time interval of the pulse can be shorter than the interval at the end of the first time interval, and possibly the interval in the second time interval. This allows the interval lengths to be adapted to the plasma dynamics.

[0028] The present invention further includes a power generator for a plasma apparatus, the power generator being: a. Generate a pulsed high-frequency signal, b. During a predetermined first time interval within a single pulse, the frequency of the high-frequency signal is changed according to a frequency sweep, and / or the amplitude of the high-frequency signal is changed according to a power sweep. c. The system is configured to generate frequency sweeps and / or power sweeps depending on at least one detected process parameter.

[0029] The method according to the present invention can be carried out particularly well using such a power generator.

[0030] A power generator may be equipped with a digital-to-analog converter for generating pulsed high-frequency signals. The signals thus generated can be amplified. This allows for control of the amplitude and frequency of the high-frequency signals. In particular, frequency sweep and power sweep can be set very easily with such a power generator.

[0031] Alternatively, the power generator may include a direct digital combiner (DDS) with a subsequent amplitude modulator for generating pulsed high-frequency signals.

[0032] The present invention further includes a plasma apparatus comprising a power generator according to the present invention, a plasma chamber, and an impedance matching unit disposed between the power generator and the plasma chamber. A detection device for detecting at least one process parameter may be provided. Furthermore, the power generator may be configured to generate frequency sweeps and / or power sweeps depending on at least one detected process parameter.

[0033] Further features and advantages of the present invention will become apparent from the following detailed description of embodiments of the invention with reference to drawings illustrating essential details of the invention, and from the claims. The features shown therein are illustrated so as to clearly visualize the special features of the present invention. Various features can be realized individually or in any combination in modifications of the invention.

[0034] Examples of the present invention are shown in the schematic diagram and will be described in more detail below. [Brief explanation of the drawing]

[0035] [Figure 1a] This graph shows the power of conventional pulsed high-frequency signals. [Figure 1b] This graph shows the frequencies of conventional pulsed high-frequency signals. [Figure 1c] Figures 1a and 1b are graphs showing the changes in the magnitude of the reflection coefficient as a result of the changes in power and frequency. [Figure 2a] This graph shows the power changes of a pulsed high-frequency signal whose amplitude is varied according to a power sweep. [Figure 2b]This graph shows the frequency progression of a high-frequency signal whose frequency is changed according to a frequency sweep. [Figure 2c] These graphs show the changes in the reflection coefficient corresponding to the signal transitions in Figures 2a and 2b. [Figure 3a] This graph shows the power progression (power sweep) of a pulsed high-frequency signal that is varied for each interval. [Figure 3b] This graph shows the frequency progression (frequency sweep) of a pulsed high-frequency signal that is varied for each section. [Figure 4] This diagram shows a simplified representation of a plasma device. [Modes for carrying out the invention]

[0036] Figure 2a shows that in the first time interval I, the amplitude of the pulsed high-frequency signal and, subsequently, the power during one pulse 10 changed. In the first time interval I, the amplitude of the high-frequency signal changes in accordance with the power sweep. On the other hand, during the second time interval II of the pulse, the amplitude of the pulsed high-frequency signal does not change. The third time interval III can represent a pulse pause in the pulsed high-frequency signal. In this case, no power is supplied to the plasma process during the pulse pause. Alternatively, in this third time interval III, it is possible that additional power different from the power in the second time interval II is supplied to the plasma process.

[0037] Basically, it is possible to switch between multiple power levels within a single pulse signal. In plasma processes, it is known that switching occurs between two, preferably three, and especially four or more power levels. For this purpose, individual time intervals (not shown in the figure) can also be defined. In each of these time intervals, the frequency can be changed according to a frequency sweep, particularly according to the frequency sweep generated as described above.

[0038] In each of these time intervals, the amplitude may be modified, either additionally or alternatively, according to a power sweep, particularly according to the power sweep generated as described above.

[0039] Figure 2b shows that the frequency of the pulsed high-frequency signal was changed during the first time interval I between one pulse 10. Thus, the frequency was changed according to the frequency sweep. In the second time interval II, the frequency also changed according to the frequency sweep. In this case, it is possible to perform a first sweep, such as a frequency sweep, in the first time interval I and a second sweep different from the first sweep, such as a power sweep, in the second time interval II, or vice versa. Alternatively, both sweeps can be performed in at least one time interval.

[0040] Figure 2c shows that the magnitude of the reflection coefficient is very large at the beginning of the first time interval I, and then decreases sharply. The decrease in the magnitude of the reflection coefficient is related to the ignition of the plasma. Through appropriate analysis, the frequency and amplitude of the pulsed high-frequency signal at which ignition occurred can be determined. To improve the ignition behavior, different frequency sweeps and / or power sweeps can be used in subsequent pulses 12. Furthermore, the time lengths of the first and / or second time intervals I and II can be changed to improve the plasma process.

[0041] Figure 3a shows a power sweep in time interval I, where the power and corresponding amplitude of the high-frequency signal have multiple sections 14 and 16. The power or amplitude is constant in each section 14 and 16. The sections 14 and 16 at the beginning of pulse 10 are shorter in duration than the sections 18 and 20 at the end of pulse 10. In this case, the section 22 at the end of the first time interval I can be longer in duration than the first section 14 at the beginning of the first time interval I. Section 22 can be the same length as or shorter than the time section 24 at the beginning of the second time interval II.

[0042] Figure 3b shows the frequency progression of a pulsed high-frequency signal. The frequency also changes within each interval from 14 to 24. Within each interval from 14 to 24, the frequency remains constant. In Figures 3a and 3b, the intervals from 14 to 24 are of the same length for power and frequency. However, it is also conceivable to select intervals from 14 to 24 with different lengths for power and frequency.

[0043] Figure 4 shows a plasma apparatus 100 equipped with a power generator 102. The power generator 102 is configured to generate a pulsed high-frequency signal, in which different frequency sweeps and / or power sweeps can be set for each pulse of the high-frequency signal. The pulsed high-frequency signal can be amplified by an amplifier 104 and supplied to the plasma chamber 108 via an impedance matching unit 106. Processing parameters are detected directly in the plasma chamber 108 by a detection device 109 and supplied to the evaluation device 110. This is indicated by arrow 112. Further process parameters, particularly electrical parameters, can be detected by a detection device 114, which is formed as a measuring device, and supplied to the evaluation device 110. This is indicated by arrow 116.

[0044] The detected processing parameters and pulsed high-frequency signals, particularly the individual pulses of the pulsed high-frequency signals, can be related to each other in the evaluation device 110. This analysis can determine whether, and by what means, the generation of pulses in the pulsed high-frequency signals needs to be modified to improve the plasma process. [Explanation of symbols]

[0045] 10 pulses 12 Subsequent pulses 100 Plasma devices 102 Power Generator 106 Impedance matching section 108 Plasma Chamber I. First time interval II. Second time interval

Claims

1. A method for igniting and / or maintaining a plasma using a pulsed high-frequency signal, a) A step of generating a pulsed high-frequency signal, b) The steps of changing the frequency of the high-frequency signal in accordance with a frequency sweep during a predetermined first time interval (I) within one pulse (10), and / or changing the amplitude of the high-frequency signal in accordance with a power sweep, c) A step of monitoring at least one process parameter of the plasma process, d) A step of determining the relationship between the process parameters and the sweep that has been performed, e) The step of detecting whether one or more monitored process parameters related to one or more sweeps take a predetermined value or are within a predetermined range, For subsequent pulses (12) and / or for a second time interval (II) of pulses, a sweep is selected based on the evaluation of one or more preceding sweeps. A method for adjusting the duration of the aforementioned time intervals (I, II) based on the evaluation of the subsequent pulse (12).

2. The method according to claim 1, characterized in that one or more sweep evaluations are performed based on the detection.

3. The method according to claim 2, characterized in that the evaluation includes the inspection of the sweep based on the detection.

4. The method according to claim 1 or 2, characterized in that different frequency sweeps and / or power sweeps are set until one or more monitored process parameters reach a predetermined value or a predetermined range of values.

5. The method according to claim 1 or 2, characterized in that, in the calibration process, a frequency sweep and / or power sweep suitable for igniting the plasma is determined.

6. A power generator (102) for a plasma device (100), The aforementioned power generator (102) a. Generate a pulsed high-frequency signal, b. During a predetermined first time interval (I) within a single pulse (10), the frequency of the high-frequency signal is changed according to a frequency sweep, and / or the amplitude of the high-frequency signal is changed according to a power sweep. c. Configured to generate frequency sweeps and / or power sweeps depending on at least one detected process parameter, For subsequent pulses (12) and / or for a second time interval (II) of pulses, a sweep is selected based on the evaluation of one or more preceding sweeps. A power generator (102) that adjusts the duration of the aforementioned time intervals (I, II) based on the evaluation of the subsequent pulse (12).

7. The power generator (102) according to claim 6, characterized in that it includes a DDS having a subsequent amplitude modulator for generating a pulsed high-frequency signal.

8. A power generator (102) for a plasma device (100), The aforementioned power generator (102) a. Generate a pulsed high-frequency signal, b. During a predetermined first time interval (I) within a single pulse (10), the frequency of the high-frequency signal is changed according to a frequency sweep, and / or the amplitude of the high-frequency signal is changed according to a power sweep. c. Configured to generate frequency sweeps and / or power sweeps depending on at least one detected process parameter, The power generator (102) includes a DDS having a subsequent amplitude modulator for generating pulsed high-frequency signals.

9. a. A power generator (102) according to any one of claims 6 to 8, b. Plasma chamber (108) and, c. A plasma apparatus (100) comprising an impedance matching unit (106) disposed between the power generator (102) and the plasma chamber (108).

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